Generally, in order to stabilize combustion generated at a combustion chamber of an engine, a method for controlling a main injection timing using a combustion pressure sensor is used. Further, in order to reduce the vibration and noise of the engine, pilot injection is introduced. In the pilot injection, before an injector performs main injection for combustion, a predetermined amount of fuel is previously injected at a predetermined point in time so that a temperature of a combustion chamber is raised and a mixture of fuel and air is improved. The pilot injection is performed at least once and may be performed multiple times in accordance with a driving condition.
Through the pilot injection, ignition delay is reduced and a rate of rise of combustion pressure is reduced. As the rate of rise of the combustion pressure is reduced, combustion noise is reduced.
However, as an operation period of an injector that injects fuel is increased, a main injection amount or a pilot injection amount may become reduced or increased by various causes. Due to the above problems, combustion pressure in the combustion chamber can become varied, and thus vibration and noise of the combustion chamber can become increased.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.